The present invention relates to a mobile communication system, a mobile station, a base station, and a packet communication method used therefor and, more particularly, to a packet communication method such as an HSDPA (High-Speed Downlink Packet Access) service in a mobile communication system.
Conventionally, in an HSDPA service, DPCHs (Dedicated Physical CHannels) [DL (downlink)/UL (uplink)] are set between a mobile station 102 and a base station 101, as shown in FIG. 26. Referring to FIG. 26, a base station control unit [e.g., an RNC (Radio Network Controller)] 103 is connected to the base station 101.
As shown in FIG. 27, the mobile station 102 always receives a 4-CH (channel) HS-SCCH (High Speed Shared Control CHannel) designated from the base station 101. The mobile station 102 detects information of the mobile station ID (identifier) contained in the HS-SCCH and determines whether the ID coincides with the reception mobile station ID of the mobile station 102 that has received the channel.
Upon detecting the reception mobile station ID of the mobile station 102 that has received the channel by the HS-SCCH, the mobile station 102 receives an HS-PDSCH (High Speed Physical Downlink Shared CHannel) transmitted with a predetermined time delay from the HS-SCCH by using control information transmitted by the HS-SCCH.
When user data to be sent or data such as upper layer control information (to be referred to as dedicated physical channel data hereinafter) to be transmitted by a dedicated physical channel is generated, the mobile station 102 and base station 101 immediately transmit the data using DPCH (UL/DL) (e.g., 3GPP TR (Technical Report) 25.858, V5.0.0, March 2002).
The above-described HSDPA is a method using high-speed packet transmission in a downlink channel. In an HSDPA service receivable state, a CPICH (Common PIlot CHannel), HS-PDSCH, HS-SCCH, and DPCH (DL) are transmitted by a downlink channel. Additionally, an HS-DPCCH (High Speed Dedicated Physical Control Channel) and DPCH (UL) are transmitted by an uplink channel.
The CPICH is a pilot signal transmitted to all mobile stations in the cell managed by the base station 101. The CPICH is transmitted from the base station 101 at a predetermined power. The CPICH is used to search for a path, estimate a transmission path, and measure the DL reception quality. The HS-PDSCH is a shared channel that transmits packets of user data. The HS-PDSCH is time-multiplexed and used between a plurality of mobile stations.
The HS-SCCH is a shared channel used to transmit control data necessary for receiving a packet transmitted by the HS-PDSCH. The HS-SCCH is time-multiplexed and used between a plurality of mobile stations. Each mobile station always receives one or a plurality of HS-SCCHs. If an HS-SCCH received by a mobile station is addressed to that mobile station, the mobile station receives an HS-PDSCH packet by using the control information in the HS-SCCH.
The DPCH (DL/UL) is constituted by a DPCCH (Dedicated Physical Control CHannel) and DPDCH (Dedicated Physical Data CHannel).
The DPCCH transmits physical layer control information such as a TPC (Transmit Power Control) bit as the transmission power control information of a paired channel or TFCI (Transport Format Combination Indication) that indicates the structure of DPDCH. The DPDCH transmits user data or dedicated physical channel data such as an upper layer control signal.
An HS-DPCCH is a dedicated physical channel that transmits a CQI (Channel Quality Indication) decided from the quality measurement result of the CPICH and ACK/NACK (ACKnowledgement/Negative ACKnowledgements) as notification confirmation information of a received packet.
In the HSDPA service, even in a standby state for a packet, a channel that transmits/receives control information representing whether a packet received by the mobile station is addressed to that station must be set. For this reason, even when the packet reception time is short, the mobile station consumes the power. Especially, the high-speed packet transmission method such as HSDPA is often used for a service such as a web browsing service in which data download is intermittently repeated. Hence, even when the packet reception time is short, power consumption of a terminal is large.
Mobile stations have no idea about the timing of packet transmission from the base station. Independently of the presence/absence of packet transmission, each mobile station must receive HS-SCCH and determine whether it contains control information addressed to that mobile station. For this reason, even when no packet is received, the terminal power is consumed.
When dedicated physical channel data to be transmitted is generated, a mobile station immediately transmits the dedicated physical channel data by using a DPCH. To do this, the DPCH must be set independently of the presence/absence of packet transmission. During this time, the terminal power is consumed.
On the other hand, both the base station and mobile stations continuously transmit/receive a DPCCH (UL/DL) even when no uplink dedicated physical channel data is transmitted. Each mobile station transmits dedicated physical channel data at an arbitrary timing. For this reason, the DPCH must be set independently of the presence/absence of dedicated physical channel data transmission. During this time, the terminal power is consumed.